Leukemia is the most common malignancy in childhood, accounting for more than 3000 new diagnoses in the U.S. each year. See Cancer Statistics Branch NCI. Cancer Incidence and Survival among Children and Adolescents: United States SEER Program, 1975-1995, 1999. Over 90% of these are acute leukemias of lymphoid or myeloid origin.
Standard methods for assessing treatment response in patients with leukemia have historically relied on repeat sampling of bone marrow and measurement of tumor burden using histopathologic and molecular approaches. These methods assess tumor regression or stabilization and, thus, do not provide evidence of early biochemical or cellular responses to therapy. For molecularly-targeted therapies, biochemical changes in the known target(s) are often assessed in an effort to identify more dynamic indicators of efficacy. However, in many cases, expression and/or activity of the presumed target(s) does not correlate with tumor response (Hamilton et al., 2005, J Clin Oncol. 23:6107-6116; Kelly et al., 2005, J Clin Oncol. 23:3923-3931; Di Maio et al., 2005, J Cell Physiol. 205:355-363), and the relevant therapeutic target is not known. Thus, the identification and validation of additional dynamic biomarkers that are accurate predictors of therapeutic efficacy allow for earlier determination of clinical response and thereby facilitate decreased exposure to ineffective and potentially toxic therapies and are useful to expedient conversion to more effective therapies when there is a poor response.
Novel non-invasive markers of leukemia assessed at diagnosis have prognostic value allowing for identification of patients in need of more intensive therapy. For example without limitation, such non-invasive markers of leukemia are desirable for early detection and staging of pediatric acute lymphoblastic leukemia (ALL) and are crucial for routine longitudinal assessment of therapy response. Thus, development of additional indicators of disease status and therapeutic response facilitates the application of effective treatment regimens on a more individualized basis.
A strong correlation between molecular abrogation during oncogenesis and changes in metabolic phenotype has been reported. For example, in various cancers AKT-induced activation of aerobic glycolysis is observed through induction of glycolytic enzymes (Elstrom et al., 2004, Cancer Res. 64:3892-3899; Young & Anderson, 2008, Breast Cancer Res. 10:202-209; DeBerardinis et al., 2008, Curr. Opinion Genet. Develop. 18:1-8). Furthermore, activation of the Ras/Raf/ERK/MAPK pathway leads to increased biosynthesis of phosphatidylcholine (the major membrane phospholipid) through up-regulation of choline kinase (Ronen et al., 2001, Br. J. Cancer 84:691-696; Beloueche-Babari et al., 2005, Cancer Res. 65:3356-3363). Additional specific metabolic markers for specific cancers have then been reported, for example without limitation, decreased N-acetyl aspartate in gliomas, decreased citrate in prostate cancer, and increased choline in breast cancer (Howe et al., 2003, Magn. Reson. Med. 49:223-232; Griffin & Shockcor, 2004, Nat. Rev. 4:551-561; Glude & Serkova, 2006, Pharmacogenomics 7:1109-1123; Serkova et al., 2007, Curr. Opin. Mol. Ther. 9:572-585). Because metabolic changes often precede detectable changes in tumor burden, metabolic changes are particularly useful as early indicators of disease and therapeutic efficacy. However, few studies investigating the utility of metabolic biomarkers in patients with acute leukemia have been reported. Nuclear magnetic resonance (NMR) spectroscopy is a technique to observe and quantify global and targeted metabolic changes in biological specimens, such as tissue biopsies and body fluids. Once established ex vivo, metabolites levels can be translated into non-invasive in vivo magnetic resonance spectroscopy (MRS) protocols (Serkova et al., 2007, Id.).
Magnetic resonance imaging (MRI) is a widely used clinical radiological modality which is a highly regarded standard for detection and follow-up of malignant tumors. With exquisite contrast resolution and ability to differentiate hematopoietic and fatty marrow, MRI is an important technique for evaluating the bone marrow non-invasively. The appearance of bone marrow in MR images depends on the pulse sequence selection and the relative amounts of cellularity, protein, water, and fat within the bone marrow. For example, spin-echo and fat-suppressed sequences have been most widely used to image bone marrow (Vogler & Murphy, 1998, Radiology 168:679-693). On T1-weighted MRI, fatty (yellow) bone marrow has higher T1-signal intensity than red bone marrow (hematopoietic). Pediatric bone marrow can display different patterns of MR signal intensity relative to adult (Mazumdar et al., 2002, Am. J. Roent. 179:1261-1266; Steinbach, 2007, Am. J. Roent. 188:1443-1445). Furthermore, the use of contrast-enhanced MRI can improve lesion conspicuity. For example, normal marrow shows minimal enhancement after administration of gadolinium chelate agents. By comparison, many malignant neoplasms exhibit an increase in signal intensity that is greater than the increase shown by normal marrow and by benign lesions.